Meet the grown-ups: Behind many of Silicon Valley's twentysomething startups, there's
a grown-up running the show. Facebook COO Sheryl Sandberg was 38 and a VP of online sales at Google when 23-year-old Mark Zuckerberg brought her in to help him turn Facebook into a profitable business.

Photo: Michael Short, Special To The Chronicle

Meet the grown-ups: Behind many of Silicon Valley's twentysomething...

John Maloney, President of Tumblr: Tumblr's twentysomething founder David Karp brought in Maloney, his former boss at the startup UrbanBaby, in 2008 to help turn the site’s millions of clicks
into millions in revenue. Maloney stepped down in 2012, after the company announced it would start selling ads.

Photo: LIONEL BONAVENTURE, AP

John Maloney, President of Tumblr: Tumblr's twentysomething founder...

Jim Barksdale, Netscape CEO: Marc Andreessen, now a Valley veteren and influential venture capitalist, was still in his twenties when he created Netscape in 1994. He brought in Barksdale, former CEO of AT&T Wireless, to head the company in 1995 and Barksdale saw the company through its IPO and sale to AOL in 1999.

Eric Schmidt, Executive Chairman at Google: Schmidt was a tech industry veteran and former CEO of Novell when Google co-founders Larry Page and Sergey Brin hired him in 2001 to take care of the business-side of things. Schmidt was Google's CEO until 2011, helping turn Google into the giant it is today.

Eric Lefkofsky, Groupon CEO: Groupon co-founder and business veteran Lefkofsky, 43, ran Groupon from behind the scenes as COO while his younger co-founder Andrew Mason served as the company's public face and CEO. Lefkofsky took the reigns as CEO after Groupon's board fired Mason last year.

Dick Costolo, Twitter CEO: Costolo, a former Google product manager, joined Twitter as COO in 2009 to help the three-year-old company monetize its millions of users. A year later, he took over as Twitter's chief executive officer to allow former CEO and co-founder
Evan Williams to focus on the product.